Web definitions

• A tag cloud or word cloud (or weighted list in visual design) is a visual depiction of user-generated tags, or simply the word content of a site, typically used to describe the content of web sites. …
  en.wikipedia.org

• A ‘tag’ is a descriptive keyword or phrase often used to categorize a piece of content. For example, an article about World of Warcraft might have the tags “World of Warcraft” and “MMORPG” because those tags accurately categorize the article’s subject matter. … webtrends.about.com